Question

The illumination a surface receives from a light source varies inversely with the square of the distance. A table lamp is 3ft from a certain work area. How far is another work area if it receives only 1/3 as much illumination as the first work area?

(W/ solution please, tnx...)

Answer 1

"The illumination a surface receives from a light source varies inversely with the square of the distance."
-----> I = k(1/d^2) , where I is the illumination, and d is the distance

or:

I1/I2 = d2^2/d1^2

I/(1/3)I) = 3^2 / d1^2

3 = 9/d^2
3d^2= 0
d^2 = 3
d = √3